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It already kind of is 8 core.

The i7 is a 4 core CPU, each core of which contains 2 execution units, so it can behave like an 8 core cpu. If you pull up activity monitor, you see 8 bars in the CPU meter.

The trouble with 8 cores is that most apps will never use that many. You have to be doing something like video encoding to begin to appreciate them - in regular day to day processing you won't see much of a speed up.
 
I don't think so, more like hexa-core instead .. next iMac refresh (or redesign, maybe?) would use Ivy Bridge Core-i intel CPU .. and only some of the highest end of them will even come with 6 core. Mainstream CPU will remain quad-core for some time.

My prediction: All next-gen iMac will still use quad-core i5 Ivy Bridge. And hexa-core will come as BTO options for high end 21.5 or 27" iMac (like i7 today). There's no way Apple would give you best CPU for standard configuration.

Of course I only talk about physical core. Hyper Threading should help a bit with performance, but alas .. only a few software can even utilize them effectively
 
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